As the IC device sizes have been shrunk to nanometer scale, the consumer electronics, like the laptop and mobile devices, have been designed to be much smaller than ever. Without suitable protection devices, the functions of these electronics could be reset or even damaged under ESD events. Currently, all consumer electronics are expected to pass the ESD test requirement of IEC 61000-4-2 standard. TVS is generally designed to bypass the ESD energy, so that the electronic systems can be prevented from ESD damages. The working principle of TVS is shown in FIG. 1. In FIG. 1, the TVS devices 10 are connected in parallel with the protected circuits 12 on the PCB (Printed Circuit Board). These TVS devices 10 would be triggered immediately when the ESD event is occurred. In that way, each TVS device 10 can provide a superiorly low resistance path for discharging the transient ESD current, so that the energy of the ESD transient current can be bypassed by the TVS devices.
FIG. 2A is a schematic diagram showing a conventional uni-directional TVS, which includes a pair of diodes (D1 and D2), a zener diode, a first pin connected with port I/O 1 and a second pin connected to ground. Specifically, the pair of diodes are connected in serial, and the zener diode is connected with the pair of diodes in parallel, and the first pin connected with port I/O 1 is connected to the pair of diodes. FIG. 2B is a schematic diagram showing a conventional bi-directional TVS, which includes a first pair of diodes (D1 and D2), a second pair of diodes (D3 and D4), a zener diode, a first pin connected with port I/O 1 and a third pin connected with port I/O 2. Specifically, the first and second pair of diodes are respectively connected in serial, the zener diode is connected with the first and second pair of diodes in parallel, and first and second pins are respectively connected the first and second pair of diodes. With the portable and mobile devices being striven towards miniaturization continuously, the PCB space for placing the conventional uni-directional/bi-directional TVS devices becomes much smaller. Therefore, it is an important purpose to decrease the chip area of the conventional TVS and maintain effectively ESD protection at present.
For the reason that the traditional TVS could not provide effective ESD protection, a need has arisen to propose a novel scheme that may adaptively provide effectively ESD protection and overcome the drawbacks of the prior art.